- 1). Sterilize your Petri dish by boiling it in water for 20 minutes. If any bacterium is already in your dish, it may reduce the effectiveness of your experiment. Remove the Petri dish from the boiling water with tongs. Set the hot Petri dish on a sterile surface so that it may cool. Do not run the hot Petri dish under cold water or it may fracture or shatter.
- 2). Pour a small amount of agar into your Petri dish. You only want enough to coat the bottom. Agar is a carbohydrate high extract that comes from red algae and is a common ingredient in most bacteria experiments. Every bacterium needs carbohydrates to grow, just like humans. Let the agar sit until it hardens. When it is completely hardened, it should look like gelatin.
- 3). Mix in a little sugar or food broth in your agar to further promote the growth of your bacteria. Avoid using salt because it can slow the bacterial process.
- 4). Swab a sample of the bacteria you would like to grow. Use a moist and sterilized cotton swab to collect some of the sample. Then swab over the harden agar in the Petri dish. This will effectively transfer the spores into their growing environment. If you do not have a sample ready, consider thinning out some bread and setting it into the Petri dish. As it ages, the bread will begin to form one of the most common and helpful bacteria called penicillin.
- 5). Set the Petri dish in a location that is constantly warm. If the temperature is too cold or it changes from hot to cold too rapidly, your sample may die. Avoid areas like windowsills because the temperature can change too quickly.
- 6). Monitor your Petri dish regularly. In the right conditions, your bacteria can grow very quickly. You may want to take a picture of the Petri dish after it is prepared and then again every time you see new growth. This will help you catalogue the rapid changes your bacterium goes through.
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